Can't run "Develop Stream Networks..."

Dear CanHuggers,

I am having problems with running my riverine flood analyses and am very much hoping you can help. The version of arcmap I am using is 10.1, with Hazus Canada 2.1. I followed the steps to after the point where I added the DEM. For the next step I must initiate "Develop Stream Network...", however the option is not selectable. I can not find out why I can't run this step. The DEM I added is one from "ASTER GDEM" (see pic). It was succesfully added. I previously also tried to use a Canadian DEM together with one from the US (because the study region crosses the border). Hope hearing from you!

Greetings, Julius